BB Test 2 Lec 4

Question 1

Movement

Four interactive systems:

Answer 1

(Deal with extraparametal - four systems) - decending axons leaving base of brain form bundel of axons pilled like pyramid - piramidal track all of the axons that then desend down spinal cord

1. Circuitry within the gray matter of the spinal cord
2. Neurons whose cells bodies lie in the cortex or brain stem (connect to spinal cord and allow complex things and contemplate them)
3. Cerebellum (no direct access to alpha motor neurons) is located on the dorsal surface of the pons (no direct access to spinal cord but connect)
4. Basal ganglia (details later) (no direct connection to spinal cord)

Question 2

Movement

Four interactive systems:

1. Circuitry within the gray matter of the spinal cord

Answer 2

1. Circuitry within the gray matter of the spinal cord
   (what is going on in spinal cord? If severed movement seses - movement could still exist but reflex)
   a. Alpha motor neurons and spinal cord interneurons
   1. The activity of alpha motor neurons (lower motor neurons) is the final common path for motor behavior
   
   2. Spinal cord interneurons receive sensory inputs as well as descending projections from higher centers; provide much of the reflexive coordination (more later)

Question 3

Movement

Four interactive systems:

2. Neurons whose cells bodies lie in the cortex or brain stem (connect to spinal cord and allow complex things and contemplate them)

Answer 3

a. Upper motor neurons
1. The axons of upper motor neurons descend to synapse with spinal cord interneurons or alpha motor neurons
2. Separate descending pathways-brain stem and cortical (more later)
3. Brain stem is involved in posture
4. Cortical pathways are essential for planning, initiating and directing voluntary movements

Question 4

Movement

Four interactive systems:

3. Cerebellum (no direct access to alpha motor neurons) is located on the dorsal surface of the pons (no direct access to spinal cord but connect)

Answer 4

a. Primary function is to compare movement commands issued by the cortex and brain stem with sensory feedback about movements that have already occurred
1. By doing so the cerebellum coordinates the components of complex movements
2. Also evidence to suggest that the cerebellum is involved in motor learning

Question 5

Organization of motor neurons in the ventral horn of the spinal cord
(5 points)

Answer 5

1. Each motor neuron innervates a single muscle
2. Each muscles is innervated by multiple motor neurons
3. All motor neurons that innervate a single muscle (motor neuron pool) are grouped together in clusters that run parallel to the long axis of the spinal cord
4. Along the A-P axis of the cord, motor neurons innervating upper extremities are located in the cervical cord, those that innervate the leg are in the lumbar, etc.
5. Along the M-L axis of a given spinal segment

Question 6

Organization of motor neurons in the ventral horn of the spinal cord

Each motor neuron innervates a single muscle

Answer 6

Alpha moto neuron and lower motor neuron - alow muscels to contract

Cell body - sends axon out - can have - spinal cord - lots of complex activity - insect cell bodies and circitry at lower motor neurons - information down brain to interneurons don’t directly control

Alpha and lower are the same thing.

Question 7

Organization of motor neurons in the ventral horn of the spinal cord

3. All motor neurons that innervate a single muscle (motor neuron pool) are grouped together in clusters that run parallel to the long axis of the spinal cord

Answer 7

a. Depending on the size of the muscle, this cluster may extend into multiple spinal segments

Question 8

Organization of motor neurons in the ventral horn of the spinal cord

5. Along the M-L axis of a given spinal segment

Answer 8

a. Neurons that innervate axial musculature are located medially
b. Neurons innervating progressively more proximal musculatures are located at corresponding more lateral positions within the cord

Question 9

Understand where motor neurons are and what they control

Answer 9

Looking at body there are things that are closer to the midline - things go out - things lying lcose to midline (Medial - close to middle) or lateral - farther from midline

Appendicular - moving to appendiges OR Distal

Axial (proximal) closer to body -

Lower motor neurons - organized medial to lateral - laterally lying will control appendiges, lyms (appindiagial musculature)
medial lying will control axial - posture

Question 10

Muscel fibors

Answer 10

lower motor neurons come down and control a subset - the distribution of the control and every muscel fiber is only controlled by one lower motor neuron - each individual muscel fiber is controlled by one neuron - each - play piano with many muscels - muscels in fo rarm alow you move finger - more motor neurons because of FINE level of control - number of motor unit - intervates predicts control - many muscels maintain posture -

Question 11

Dirmitome

Answer 11

Is controlled by perticular spinal cord - 31 on each side - regions of body - controlled by one spinal nerve! BUT small amount of (say C2 or C3 or C6) so that even if something happened there would be a bit of ability to control area of dermitome - how does that happen anatomically? If cell bodies for lower motor neurons - most are concentrated in segment that controls region but others are else where to serve as a fail state - distribute into neighboring segments

Question 12

Motor Unit (motor neuron and its corresponding muscle fiber)

1. Types of motor units based on:

Answer 12

1. Speed of contraction
2. Maximum tension generated
3. Degree to which they fatigue

Question 13

Motor Unit (motor neuron and its corresponding muscle fiber)

Types

Answer 13

Fast fatigable (FF) motor units
Slow (S) motor units
Fast fatigue-resistant (FR) motor units

Question 14

Fast fatigable (FF) motor units

Answer 14

1. Contract and relax rapidly
2. Generate largest force
3. Fatigue after a few minute of repeated stimulation

can get tired in a couple minutes Not maximum load - but in range of capabilities Curl a weight

Question 15

Slow (S) motor units

Answer 15

1. Fatigue resistant
2. Contract slowly
3. Fraction of FF’s force

don’t generate lot of force but funsction over long periods of time

Question 16

Fast fatigue-resistant (FR) motor units

Answer 16

1. 2x force of Slow
2. More fatigue resistant than FF
3. Not as fast as FF

don’t retract as quickly - MOST muscels varying proportions of the motor units

Question 17

Motor Neoron Example

Muscles and motor units

Answer 17

For example, posture, our vetigral collum is posterior - gravity wants to pull us forward - tethering collum to pelvus - functionally can’t fatigue - type of muscel lots of S - BUT the ones in the eye muscels - moves quickly more FF - our muscels have a distribution of each type

Individuals muscles include varying proportions of each type of motor unit. Muscles involved in posture will have a high proportion of S type, whereas those generating rapid movements (e.g., extraocular muscles) have a high proportion of FF units.